It is not accurate to characterize all atheists as making their own decisions or to characterize all Christians as simply following the majority. People of all faiths (or none) are different from one another and can have different reasons for holding the beliefs that they hold.
It is true that atheism is a much less common choice than Christianity in the United States today. However, that does not mean that all atheists come to atheism through choice or that all Christians simply follow the masses. It is very possible that a person could come to be an atheist simply because his or her parents were atheists.
So, while it is easier to simply “fall into” being Christian, it is possible to become an atheist without a major decision and it is possible for a person to choose Christianity only after much thought.